In the repair and realignment of damaged vehicle bodies or frames, it is common practice to pull the crumpled or damaged body shell, or a bent frame, into a shape or position approximating the original configuration, and finishing repairs then restore the body or frame to the proper condition. In such pulling operation, large forces are generated, and it is essential that the vehicle be firmly anchored to prevent movement or slippage during the pulling operation. As a consequence, prior art arrangements generally comprise a longitudinal frame upon which are mounted and secured thereto transverse beam members which are, in turn, secured to the vehicle body, so that the vehicle body is firmly held against movement in a position above the longitudinal frame with its longitudinal axis parallel to the longitudinal axis of the frame, and with its wheels clear of the frame. Mounted on the frame, either at the front or rear thereof, or at the sides is a pulling apparatus, of which there may be several, which comprises a flexible member, such as a chain, having one end anchored to the frame and the other end hooked or otherwise attached to the portion of the vehicle to be pulled. Tensioning means, such as a hydraulic piston and cylinder ram swivelly mounted at one end to the frame with the other end bearing against the chain intermediate its ends applies tension to the chain, forcing it to pull the damaged portion of the vehicle into shape. As thus far described, such an alignment apparatus is shown and described in U.S. Pat. Nos. 4,023,394 and 4,050,287, both of Borup.
In the just described chain tensioning arrangement it quite commonly occurs that point of anchor of the chain end to the frame, the point of mounting of the ram to the frame, and the point of attachment of the chain to the vehicle are not always longitudinally aligned, nor can they be so aligned. Unless these three points are aligned to be in approximately the same vertical plane, when tension is applied the swivelly mounted piston and cylinder ram tends to tilt or cock. When the points lie in a vertical plane all of the force generated by the ram is directed toward pulling the vehicle body straight along a line lying in the plane. If, however, the ram is tilted, there is a component of force directed transversely to the pulling direction with the consequence that the maximum available pulling force is not utilized, which, in some cases, can result in unsatisfactory or incomplete straightening of the vehicle body or frame.
In the prior art arrangements, the tilting of the ram mechanism is especially common when the apparatus is used to pull the side of the vehicle body or frame, primarily because of a scarcity of places on the apparatus frame at which to mount the ram and to anchor the chain end. In addition, in some instances the point of attachment to the vehicle may be remote from the point of anchoring of the chain, necessitating an unduly long chain.